1. Field of the Invention
The present invention relates generally to multi-cylinder internal combustion engines and more specifically to an induction system for such an engine which enables good inertia supercharging during both high and low engine speed operation.
2. Description of the Prior Art
FIG. 1 of the drawings shows an induction arrangement disclosed in Japanese Patent Application First Provisional Publication No. 56-115818. This arrangement as shown, comprises a single elongate collector 10 which communicates with a surge tank 12 via first and second interconnecting induction conduits 13, 14 Each of the engine cylinders #1 to #6 communicate with the collector 10 via branch runners 15a-15f. A valve 16 is disposed in the collector 10 so as to divide the same into first and second sections 10A, 10B. The first section 10A communicates with a first group of engine cylinders #1 to #3 while the second section 10B communicates with the remaining cylinders #4 to #6. When the engine is operating at low speed valve 16 is closed.
The ignition order of the first and second groups of cylinders are respectively discontinuous. Accordingly, when the engine is operating at low engine speed and the valve 16 is closed the first and second groups of cylinders aspirate through mutually independent induction systems. The dimensions of the conduiting etc., of the induction arrangement is selected so that resonance characteristics of the two "quasi" independent systems are such as to coincide with the induction pressure pulsations under low engine speed condition and thus induce good inertia ram charging (supercharging). Upon the engine speed exceeding a predetermined level valve 16 opens and induces the situation wherein the natural frequency of the single enlarged system under such conditions matches the induction pressure pulstations which occur at this time.
However, this arrangement encounters the drawback in that although the system is relatively simple, upon opening of valve 16 the charging effect provided in branch runners 15c and 15d which are located close to the valve and the charging effect provided at branch runners 15a and 15f (remote from valve 16) are not the same. Accordingly, charging efficiency varies from one cylinder to another and optimal engine performance is not obtained.
Further examples of the above type of induction system are found in Japanese Patent Utility Model First Prov. Pub. No. 58-129063 and Japanese Patent Utility Model Second Prov. Pub. No. 46-21123.